Currently, R12 is used in closed loop refrigeration systems; many of these systems are automotive air-conditioning systems. R12 refrigeration systems generally use mineral oils to lubricate the compressor. Mineral oil is typically paraffin oil or naphthenic oil.
A problem which faces the industry is that R12, which contains chlorine, and currently used lubricants such as mineral oil, which contains hydrogen, react to form acids such as hydrogen chloride and hydrogen fluoride and simultaneously, the R12 is converted to R22. Such reactions are undesirable because the acids which form destroy the metallic components of a refrigeration system and also cause the breakdown of the mineral oil. As such, the need exists in the art for an additive which substantially minimizes the reaction of R12 with hydrogen-contributing lubricants such as mineral oil.
R134a has been mentioned as a possible replacement for R12 because concern over potential depletion of the ozone layer exists. R134a has properties similar to those of R12 so that it is possible to substitute R134a for R12 with minimal changes in equipment being required. The symmetrical isomer of R134a is R134 (1,1,2,2-tetrafluoroethane); the isomer is also similar in properties and may also be used. Consequently, it should be understood that in the following discussion, "tetrafluoroethane" will refer to both R134 and R134a.
A unique problem arises in such a substitution. As mentioned earlier, refrigeration systems which use R12 generally use mineral oils to lubricate the compressor; the present discussion does not apply to absorption refrigeration equipment. See for example the discussion in Chapter 32 of the 1980 ASHRAE Systems Handbook. R12 is completely miscible with such oils throughout the entire range of refrigeration system temperatures which may range from about -45.6.degree. C. to 65.6.degree. C. Consequently, oil which dissolves in the refrigerant travels around the refrigerant loop and generally returns with the refrigerant to the compressor. The oil does not separate during condensation, although it may accumulate because low temperatures exist when the refrigerant is evaporated. At the same time, the oil which lubricates the compressor contains some refrigerant which may affect its lubricating property.
It is known in the industry that chlorodifluoromethane (known in the art as R22) and chlorodifluoromethane/1-chloro-1,1,2,2,2-pentafluoroethane (known in the art as R502) are not completely miscible in common refrigeration oils. See Downing, FLUOROCARBONS REFRIGERANT HANDBOOK, Page 13. A solution to this problem has been the use of alkylated benzene oils. Such oils are immiscible in R134a and are not useful therewith. This problem is most severe at low temperatures when a separated oil layer would have a very high viscosity. Problems of oil returning to the compressor would be severe.
R134a is not miscible with mineral oils; consequently, different lubricants will be required for use with R134a. However, as mentioned above, no changes to equipment should be necessary when the refrigerant substitution is made. If the lubricant separates from the refrigerant, it is expected that serious operating problems could result. For example, the compressor could be inadequately lubricated if refrigerant replaces the lubricant. Significant problems in other equipment also could result if a lubricant phase separates from the refrigerant during condensation, expansion, or evaporation. These problems are expected to be most serious in automotive air-conditioning systems because the compressors are not separately lubricated and a mixture of refrigerant and lubricant circulates throughout the entire system.
Small amounts of lubricants may be soluble in R134a over a wide range of temperatures, but as the concentration of the lubricant increases, the temperature range over which complete miscibility occurs, i.e., only one liquid phase is present, narrows substantially. For any composition, two consolute temperatures, i.e., a lower and a higher temperature, may exist. That is, a relatively low temperature below which two distinct liquid phases are present and above which the two phases become miscible and a higher temperature at which the single phase disappears and two phases appear again may exist. A diagram of such a system for R502 refrigerant is shown as FIG. 2 in the Kruse et al. paper mentioned above. A range of temperatures where one phase is present exists and while it would be desirable that a refrigeration system operate within such a range, it has been found that for typical compositions, the miscible range of lubricants with R134a is not wide enough to encompass the typical refrigeration temperatures.
In response to the foregoing need in the art, lubricants which are miscible with R134a have been developed. See commonly assigned U.S. Pat. Nos. 4,755,316; 4,900,463; and 4,975,212.
The industry faces another problem in the substitution of R134a for R12. Upon the conversion of a refrigeration system to R134a and the addition of substitute hydrogen-contributing lubricant which is miscible with R134a to the system, the industry is concerned that any R12 remaining in the system would be incompatible with the substitute hydrogen-contributing lubricant. It is believed that R12, which contains chlorine, and the hydrogen-contributing substitute lubricants react to form acids such as hydrogen chloride and hydrogen fluoride and simultaneously, the R12 is converted to R22. Such reactions are undesirable because the acids which form destroy the metallic components of a refrigeration system and cause the breakdown of the lubricant.
Although all of the R12 in a system being retrofitted for R134a and hydrogen-contributing lubricant miscible with R134a could be removed, the industry is seeking a more acceptable solution to the problem.
If an additive substantially minimized the reaction of R12 with currently used hydrogen-contributing lubricants and also hydrogen-contributing lubricants which are miscible with R134a, any R12 remaining in a system which is being retrofitted with R134 would not have to be removed from the system and the preceding problem would be substantially eliminated. As such, the need exists in the art for an additive which prevents the reaction of R12 with hydrogen-contributing lubricants.
In an attempt to solve this problem, we considered epoxides as taught by Kokai Patent Publication 179,699 published Oct. 12, 1984; and Kokai Patent Publication 281,199 published Dec. 11, 1988. As shown in Comparative C below, we added epoxides to compositions of R12 and mineral oil and found that epoxides alone were ineffective in substantially reducing the reaction of R12 with mineral oil. As shown in Comparative H below, we added epoxides to compositions of R12 and hydrogen-contributing lubricants miscible with R134a and found that epoxides were ineffective in substantially reducing the reaction of R12 with the lubricants.
Also in an attempt to solve this problem, we considered phenols as listed in commonly assigned U.S. Pat. No. 4,755,316; Kokai Patent Publication 281,199 published Dec. 11, 1988; U.S. Pat. Nos. 4,812,246 and 4,851,144; commonly assigned U.S. Pat. No. 4,900,463; Kokai Patent Publication 102,296 published Apr. 13, 1990; U.S. Pat. No. 4,959,169; and commonly assigned U.S. Pat. No. 4,975,212. As shown in Comparative B below, we added phenols to compositions of R12 and mineral oil and found that the hindered phenols alone were ineffective in substantially reducing the reaction of R12 with mineral oil. As shown in Comparatives G and I below, we added phenols to compositions of R12 and hydrogen-contributing lubricants miscible with R134a and found that phenols alone were ineffective in substantially reducing the reaction of R12 with the lubricants.
We were then surprised to find that the combination of aromatic epoxide and phenol is effective in substantially reducing the reaction of R12 with mineral oil. We were also surprised to find that the combination of aromatic epoxide and phenol is effective in substantially reducing the reaction of R12 with hydrogen-contributing lubricants which are miscible with R134a. We were also surprised to find that the combination of aromatic epoxide and phenol is effective in substantially reducing the reaction of R12 with mineral oil and hydrogen-contributing lubricants which are miscible with R134a.
U.S. Pat. Nos. 4,248,726; 4,267,064; and 4,431,557 teach the addition of epoxides to compositions of refrigerants and lubricants. The references also teach that known additives such as phenol or amine type antioxidants; sulphur or phosphorus type oiliness improvers; silicone type antifoam agents; metal deactivators such as benzotriazole, amines, and acid esters; and load carrying additives such as phosphoric acid esters, phosphorous acid esters, thiophosphoric acid esters, organic sulfur compounds, and organic halogen compounds can be used. These references do not teach or suggest the present invention.
U.S. Pat. No. 4,948,525 teaches that known refrigerator oil additives such as phenol-type antioxidants such as di-tert-butyl-p-cresol; amine-type antioxidants such as phenyl-.alpha.-naphthylamine and N,N'-di(2-naphthyl)-p-phenylenediamine; load resistant additives such as zinc dithiophosphate, chlorinated paraffin, fatty acids, and sulfur type load resistant compounds; silicone-type antifoaming agents; metal inactivators such as benzotriazole; and hydrogen chloride captors such as glycidyl methacrylate and phosphite esters may be used in refrigeration compositions. The reference states that these additives may be used singly or jointly but does not teach or suggest the present invention.